1. Field of the Invention
This invention relates to a method of shaping semisolid metals. More particularly, the invention relates to a method of shaping semisolid metals, in which a liquid alloy having crystal nuclei at a temperature not lower than the liquidus temperature or a partially solid, partially liquid alloy having crystal nuclei at a temperature not lower than a molding temperature is fed into an insulated vessel having a heat insulating effect, holding the alloy for a period from 5 seconds to 60 minutes as it is cooled to the molding temperature where a specified liquid fraction is established, thereby generating fine primary crystals in the alloy solution and the alloy is shaped under pressure. The invention also relates to an apparatus for implementing this method.
More particularly, the invention further relates to a method of shaping semisolid metals, in which a liquid alloy having crystal nuclei and at a temperature not lower than the liquidus temperature or a partially solid, partially liquid alloy having crystal nuclei and at a temperature less than the liquidus temperature but not lower than the molding temperature is poured into a holding vessel, cooled at an average cooling rate in a specified range and held as such until just prior to the start of shaping under pressure, whereby fine primary crystals are generated in the alloy solution and the alloy within the holding vessel is temperature adjusted by induction heating such that the temperatures of various parts of the alloy fall within the desired molding temperature range for the establishment of a specified fraction liquid not later than the start of shaping and the alloy is recovered from the holding vessel, supplied into a forming mold and shaped under pressure.
The invention also relates to a method of shaping semisolid metals, in which a molten aluminum or magnesium alloy containing a crystal grain refiner which is maintained superheated to less than 50xc2x0 C. above the liquidus temperature is poured directly into a holding vessel without using any cooling jig and held for a period from 30 seconds to 30 minutes as the melt is cooled to the molding temperature where a specified liquid fraction is established such that the temperature of the poured alloy which is either liquid and superheated to less than 10xc2x0 C. above the liquidus temperature or which is partially solid, partially liquid and less than 5xc2x0 C. below the liquidus temperature is allowed to decrease from the initial level and pass through a temperature zone 5xc2x0 C. below the liquidus temperature within 10 minutes, whereby fine primary crystals are generated in the alloy solution, and the alloy within said holding vessel is temperature adjusted by induction heating such that the temperatures of various parts of the alloy fall within the desired molding temperature range for the establishment of a specified fraction liquid not later than the start of shaping and the alloy is recovered from the holding vessel, supplied into a forming mold and shaped under pressure.
2. Background Information
Various methods for shaping semisolid metals are known in the art. A thixo-casting process is drawing researchers"" attention these days since it involves a fewer molding defects and segregations, produces uniform metallographic structures and features longer mold lives but shorter molding cycles than the existing casting techniques. The billets used in this molding method (A) are characterized by spheroidized structures obtained by either performing mechanical or electromagnetic agitation in temperature ranges that produce semisolid metals or by taking advantage of recrystallization of worked metals. On the other hand, raw materials cast by the existing methods may be molded in a semisolid state. There are three examples of this approach; the first two concern magnesium alloys that will easily produce an equiaxed microstructure and Zr is added to induce the formation of finer crystals [method (B)] or a carbonaceous refiner is added for the same purpose [method (C)]; the third approach concerns aluminum alloys and a master alloy comprising an Al-5% Ti-1% B system is added as a refiner in amounts ranging from 2-10 times the conventional amount [method (D)]. The raw materials prepared by these methods are heated to temperature ranges that produce semisolid metals and the resulting primary crystals are spheroidized before molding. It is also known that alloys within a solubility limit are heated fairly rapidly up to a temperature near the solidus line and, thereafter, in order to ensure a uniform temperature profile through the raw material while avoiding local melting, the alloy is slowly heated to an appropriate temperature beyond the solidus line so that the material becomes sufficiently soft to be molded [method (E)]. A method is also known, in which molten aluminum at about 700xc2x0 C. is cast to flow down an inclined cooling plate to form partialy molten aluminum, which is collected in a vessel [method (F)].
These methods in which billets are molded after they are heated to temperatures that produce semisolid metals are in sharp contrast with a rheo-casting process (G), in which molten metals containing spherical primary crystals are produced continuously and molded as such without being solidified to billets. It is also known to form a rheo-casting slurry by a method in which a metal which is at least partially solid, partially liquid and which is obtained by bringing a molten metal into contact with a chiller and inclined chiller is held in a temperature range that produces a semisolid metal [method (H)].
Further, a casting apparatus (I) is known which produces a partially solidified billet by cooling a metal in a billet case either from the outside of a vessel or with ultrasonic vibrations being applied directly to the interior of the vessel and the billet is taken out of the case and shaped either as such or after reheating with r-f induction heater.
However, the above-described conventional methods have their own problems. Method (A) is cumbersome and the production cost is high irrespective of whether the agitation or recrystallization technique is utilized. When applied to magnesium alloys, method (B) is economically disadvantageous since Zr is an expensive element and concerning method (C), in order to ensure that carbonaceous refiners will exhibit their function to the fullest extent, the addition of Be as an oxidation control element has to be reduced to a level as low as about 7 ppm, but then the alloy is prone to burn by oxidation during the heat treatment just prior to molding and this is inconvenient in operations.
In the case of aluminum alloys, about 500 xcexcm is the size that can be achieved by the mere addition of refiners and it is not easy to obtain crystal grains finer than 100 xcexcm to 200 xcexcm. To solve this problem, increased amounts of refiners are added in method (D), but this is industrially difficult to implement because the added refiners are prone to settle on the bottom of the furnace; furthermore, the method is costly. Method (E) is a thixo-casting process which is characterized by heating the raw material slowly after the temperature has exceeded the solidus line such that the raw material is uniformly heated and spheroidized. In fact, however, an ordinary dendritic microstructure will not transform to a thixotropic structure (in which the primary dendrites have been spheroidized) upon heating. According to method (F), partially molten aluminum having spherical particles in the microstructure can be obtained conveniently but no conditions are available that provide for direct shaping.
Moreover, thixo-casting methods (A)-(F) have a common problem in that they are more costly than the existing casting methods because in order to perform molding in the semisolid state, the liquid phase must first be solidified to prepare a billet, which is heated again to a temperature range that produces a semisolid metal. In addition, the billets as the starting material are difficult to recycle and the liquid fraction cannot be increased to a very high level because of handling considerations. In contrast, method (G) which continuously generates and supplies a molten metal containing spherical primary crystals is more advantageous than the thixocasting approach from the viewpoint of cost and energy but, on the other hand, the machine to be installed for producing a metal material consisting of a spherical structure and a liquid phase requires cumbersome procedures to assure effective operative association with the casting machine to yield the final product. Specifically, if the casting machine fails, difficulty arises in the processing of the semisolid metal.
Method (E) which holds the chilled metal for a specified time in a temperature range that produces a semisolid metal has the following problem. Unlike the thixo-casting approach which is characterized by solidification into billets, reheating and subsequent shaping, the method (H) involves direct shaping of the semisolid metal obtained by holding in the specified temperature range for a specified time and in order to realize industrial continuous operations, it is necessary that an alloy having a good enough temperature profile to establish a specified liquid fraction suitable for shaping should be formed within a short time. However, the desired rheo-casting semisolid metal which has a fraction liquid and a temperature profile that are suitable for shaping cannot be obtained by merely holding the cooled metal in the specified temperature range for a specified period.
In method (I), a case for cooling the metal in a vessel is employed but the top and the bottom portions of the metal in the vessel will cool faster than the center and it is difficult to produce a partially solidified billet having a uniform temperature profile and immediate shaping will yield a product of nonuniform structure. Furthermore, considering the need to satisfy the requirement that the partially solidified billet as taken out of the billet case has such a temperature that the initial state of the billet is maintained, it is difficult for the liquid fraction of the partially solidified billet to exceed 50% and the maximum that can be attained practically is no more than about 40%, which makes it necessary to give special considerations in determining injection and other conditions for shaping by diecasting. If the liquid fraction of the billet has dropped below 40%, it could be reheated with a r-f induction heater but is is still difficult to attain a liquid fraction in excess of 50% and special considerations must be made in injection and other shaping conditions. In addition, eliminating any significant temperature uneveness that has occurred within the partially solidified billet is a time-consuming practice and it is required, although for only a short time, that the r-f induction heater produce a high power comparable to that required in thixo-casting. In addition it is necessary to install multiple units of the r-f induction heater in order to achieve continuous operation in short cycles.
Another problem with the industrial practice of shaping semisolid metals in a continuous manner is that if a trouble occurs in the casting machine, the semisolid metal may occasionally be held in a specified temperature range for a period longer than the prescribed time. Unless a certain problem occurs in the metallographic structure, it is desired that the semisolid metal be maintained at a specified temperature; in practice, however, particularly in the thixo-casting process where the semisolid metal is held with its temperature elevated from room temperature, the metallographic structure becomes coarse and the billets are considerably deformed (progressively increase in diameter toward the bottom) and, in addition, such billets are usually discarded, which is simply a waste in resources, unless their temperatures are individually controlled.
The present invention has been accomplished under these circumstances of the prior art and has an object is to provide a method that does not use billets or any cumbersome procedures, but which ensures convenience and ease in the production of semisolid metals having fine primary crystals and shaping them under pressure.
Another object of the invention is to provide an apparatus that can implement this method.
It is a further object of the present invention to provide a method to produce semisolid metal (including those which have higher values of liquid fraction than what are obtained by the conventional thixo-casting process) which are suitable for subsequent shaping on account of both a uniform structure containing spheroidized primary crystals and uniform temperature profile in a convenient and easy manner with such great rapidity that the power requirement of the r-f induction heater is no more than 50% of what is commonly expended in shaping by the thixo-casting process, the semisolid metals being subsequently shaped under pressure.
One of the objects of the invention can be attained by the method of shaping a semisolid metal according to a first embodiment of the present invention, in which a liquid alloy having crystal nuclei at a temperature not lower than the liquidus temperature or a partially solid, partially liquid alloy having crystal nuclei at a temperature not lower than a molding temperature is fed into an insulated vessel having a heat insulating effect, held in said insulated vessel for a period from 5 seconds to 60 minutes as it is cooled to the molding temperature where a specified fraction liquid is established, thereby crystallizing primary crystals in the alloy solution, and the alloy is fed into a forming mold, where it is shaped under pressure.
According to a second embodiment of the present invention, the crystal nuclei in the first embodiment of the present invention are generated by contacting the molten alloy with a surface of a jig at a temperature lower than the melting point of the alloy which has been maintained superheated to less than 300xc2x0 C. above the liquidus temperature.
According to a third embodiment of the present invention, the jig in the second embodiment of the present invention is a metallic or nonmetallic jig, or a metallic jig having a surface coated with nonmetallic materials or semiconductors, or a metallic jig compounded of nonmetallic materials or semiconductors, with the jig being adapted to be coolable from either inside or outside.
According to a fourth embodiment of the present invention, the crystal nuclei in the first or second embodiments of the present invention are generated by applying vibrations to the molten metal in contact with either the jig or the insulated vessel or both.
According to a fifth embodiment of the present invention, the alloy in the first or second embodiments of the present invention is an aluminum alloy of a composition within a maximum solubility limit or a hypoeutectic aluminum alloy of a composition at or above a maximum solubility limit.
According to a sixth embodiment of the present invention, the alloy in the first or second embodiments of the present invention is a magnesium alloy of a composition within a maximum solubility limit.
According to a seventh embodiment of the present invention, the aluminum alloy in the fifth embodiment of the present invention has 0.001%-0.01% B and 0.005%-0.3% Ti added thereto.
According to an eighth embodiment of the present invention, the magnesium alloy in the sixth embodiment of the present invention is one having 0.005%-0.1% Sr added thereto, or one having 0.01%-1.5% Si and 0.005%-0.1% Sr added thereto, or one having 0.05%-0.3% Ca added thereto.
According to a ninth embodiment of the present invention, a molten aluminum alloy held superheated to less than 100xc2x0 C. above the liquidus temperature is directly poured into an insulated vessel without using a jig.
According to a tenth embodiment of the present invention, a molten magnesium alloy held superheated to less than 100xc2x0 C. above the liquidus temperature is directly poured into an insulated vessel without using a jig.
According to a eleventh embodiment of the present invention, a liquid alloy having crystal nuclei that has been superheated by a degree (Xxc2x0 C.) of less than 10xc2x0 C. above the liquidus line is maintained in an insulated vessel for a period from 5 seconds to 60 minutes as it is cooled to a molding temperature where a specified liquid fraction is established, such that the cooling from the initial temperature at which the alloy is held in the insulated vessel to its liquidus temperature is completed within a time shorter than the time Y (in minutes) calculated by the relationship Y=10xe2x88x92X and that the period of cooling from said initial temperature to a temperature 5xc2x0 C. lower than the liquidus temperature is not longer than 15 minutes, whereby fine primary crystals are crystallized in the alloy solution, which is then fed into a forming mold, where it is shaped under pressure.
According to a twelfth embodiment of the present invention, a partially solid, partially liquid alloy having crystal nuclei at a temperature not lower than a molding temperature is maintained within an insulated vessel for a period from 5 seconds to 60 minutes as it is cooled to the molding temperature where a specified liquid fraction is established, such that the period of cooling from the initial temperature at which the alloy is held in the insulated vessel to a temperature 5xc2x0 C. lower than its liquidus temperature is not longer than 15 minutes, whereby fine primary crystals are crystallized in the alloy solution, which is then fed into a forming mold, where it is shaped under pressure.
According to a thirteenth embodiment of the present invention, the crystal nuclei in the eleventh or twelfth embodiments of the present invention are generated by holding a molten alloy superheated to less than 300xc2x0 C. above the liquidus temperature and contacting the melt with a surface of a jig at a lower temperature than its melting point.
One of the objects of the invention can be attained by the apparatus in a fourteenth embodiment of the present invention which is for producing a semisolid forming metal having fine primary crystals dispersed in a liquid phase, the apparatus comprising a nucleus generating section that causes a molten metal to contact a cooling jig to generate crystal nuclei in the solution and a crystal generating section having an insulated vessel in which the metal obtained in the nucleus generating section is maintained as it is cooled to a molding temperature at which the metal is partially solid, partially liquid.
According to a fifteenth embodiment of the present invention, the cooling jig in the nucleus generating section in the fourteenth embodiment of the present invention is either an inclined flat plate that has an internal channel for a cooling medium and that has a pair of weirs provided on the top surface parallel to the flow of the melt, or a cylindrical or semicylindrical tube.
According to a sixteenth embodiment of the present invention, a liquid alloy having crystal nuclei at a temperature not lower than the liquidus temperature or a partially solid, partially liquid having crystal nuclei at a temperature not lower than a molding temperature is poured into a vessel so that it is cooled to a temperature at which a solid fraction appropriate for shaping is established, the vessel being adapted to be heatable or coolable from either inside or outside, being made of a material having a thermal conductivity of at least 1.0 kcal/hrxc2x7mxc2x7xc2x0 C. (at room temperature) and being maintained at a temperature not higher than the liquidus temperature of the alloy prior to its pouring, and the alloy is poured into the vessel in such a manner that fine, nondendritic primary crystals are crystallized in the alloy solution and that the alloy is cooled rapidly enough to be provided with a uniform temperature profile in the vessel, and the alloy, after being cooled, is fed into a forming mold, where it is shaped under pressure.
According to a seventeenth embodiment of the present invention, the step of cooling the alloy in the sixteenth embodiment of the present invention is performed with the top and bottom portions of the vessel being heated by a greater degree than the middle portion or heat-retained with a heat-retaining material having a thermal conductivity of less than 1.0 kcal/hrxc2x7mxc2x7xc2x0 C. or with either the top or bottom portion of the vessel being heated, while the remainder is heat-retained.
According to an eighteenth embodiment of the present invention, the step of cooling the alloy in the sixteenth embodiment of the present invention is performed with the vessel holding the alloy being accommodated in an outer vessel that is capable of accommodating the alloy holding vessel and that has a smaller thermal conductivity than the holding vessel, or that has a thermal conductivity equal to or greater than that of the holding vessel and which has a higher initial temperature than the holding vessel, or that is spaced from the holding vessel by a gas-filled gap, at a sufficiently rapid cooling rate to provide a uniform temperature profile through the alloy in the holding vessel no later than the start of the shaping step.
According to a nineteenth embodiment of the present invention, there is provided a method of managing the temperature of a semisolid metal slurry for use in molding equipment in which a molten metal containing a large number of crystal nuclei is poured into a vessel, where it is cooled to produce a semisolid metal slurry containing both a solid and a liquid phase in specified amounts, the slurry being subsequently fed into a molding machine for shaping under pressure, which method is characterized in that the vessel for holding the molten metal is temperature-managed such as to establish a preset desired temperature prior to the pouring of the molten metal and such that the molten metal is cooled at an intended rate after said molten metal is poured into the vessel.
According to a twentieth embodiment of the present invention, there is provided an apparatus for managing the temperature of a semisolid metal slurry to be used in molding equipment in which a molten metal containing a large number of crystal nuclei is poured from a melt holding furnace into a vessel, where it is cooled to produce a semisolid metal slurry containing both a solid and a liquid phase in specified amounts and in which the slurry is directly fed into a molding machine for shaping under pressure, which apparatus is further characterized by comprising a vessel for holding the molten metal, a vessel temperature control section for managing the temperature of the vessel, a semisolid metal cooling section for managing the temperature of the as-poured molten metal such that it is cooled at an intended rate, and a vessel transport mechanism comprising basically a robot for gripping, moving and transporting the vessel and a conveyor for carrying, moving and transporting the vessel.
According to a twenty-first embodiment of the present invention, the vessel temperature control section in the twentieth embodiment of the present invention comprises a vessel cooling furnace for cooling the vessel to an ambient temperature not higher than a target temperature for the vessel and a vessel heat-retaining furnace for maintaining the vessel at an ambient temperature equal to the target temperature.
According to a twenty-second embodiment of the present invention, the semisolid metal cooling section in the twentieth embodiment of the present invention comprises a semisolid metal cooling furnace and a semisolid metal annealing furnace for managing the temperature to be higher than the temperature in the semisolid metal cooling furnace.
According to-a twenty-third embodiment of the present invention, the semisolid metal cooling furnace in the semisolid metal cooling section in the twenty-second embodiment of the present invention is such that the area around the vessel carried on the conveyor device which is moved to pass through the furnace is partitioned into three regions, the upper, middle and lower parts, by means of two pairs of heat insulating plates, one pair comprising an upper right and an upper left plate and the other pair comprising a lower right and a lower left plate, with a heater being installed in both the upper and lower parts for heating the two parts at a higher temperature than hot air to be supplied to the central part.
According to a twenty-fourth embodiment of the present invention, a preheating furnace is installed at a stage prior to the semisolid metal cooling furnace in the twenty-second embodiment of the present invention to ensure that both a plinth having a lower thermal conductivity than the vessel and which carries the vessel before it is directed to the semisolid metal cooling furnace and a lid having a lower thermal conductivity than the vessel and which is to be placed to cover it after it accommodates the molten metal are preheated by being moved to pass through the preheating furnace in advance.
According to a twenty-fifth embodiment of the present invention, the semisolid metal cooling furnace is equipped with a control unit with which the temperature or the velocity of hot air to be supplied into the semisolid metal cooling furnace is controlled to vary with the lapse of time.
According to a twenty-sixth embodiment of the present invention, the semisolid metal cooling furnace in the twenty-second embodiment of the present invention comprises an array of housings each accommodating the vessel as it contains the molten metal and being equipped with an openable cover and hot air feed/exhaust pipes, as well as a mechanism by which a receptacle for carrying the vessel is rotated about a vertical shaft.
According to a twenty-seventh embodiment of the present invention, a vibrator for vibrating the receptacle in the twenty-sixth embodiment of the present invention is provided for each housing.
According to a twenty-eighth embodiment of the present invention, the semisolid metal cooling furnace for treating the molten metal as poured into a vessel having a thermal conductivity of at least 1.0 kcal/hrxc2x7mxc2x7xc2x0 C. is supplied with hot air having a temperature in the range from 150xc2x0 C. to 350xc2x0 C. for aluminum alloys and from 200xc2x0 C. to 450xc2x0 C. for magnesium alloys.
According to a twenty-ninth embodiment of the present invention, the semisolid metal cooling furnace for treating the molten metal as poured into a vessel having a thermal conductivity of less than 1.0 kcal/hrxc2x7mxc2x7xc2x0 C. is supplied with hot air having a temperature in range from 50C to 200xc2x0 C. for aluminum alloys and from 100xc2x0 C. to 250xc2x0 C. for magnesium alloys.
According to a thirtieth embodiment of the present invention, the molten metal as poured into the insulated vessel in the first or second embodiments of the present invention is isolated from the ambient atmosphere by closing the top surface of the vessel with an insulating lid having a heat insulating effect as long as the molten metal is held within the vessel until the molding temperature is reached.
According to a thirty-first embodiment of the present invention, the alloy in the first or second embodiments of the present invention is a zinc alloy.
According to a thirty-second embodiment of the present invention, the alloy in the first or second embodiments of the present invention is a hypereutectic Alxe2x80x94Si alloy having 0.005%-0.03% P added thereto.or a hypereutectic Alxe2x80x94Si alloy containing 0.005%-0.03% P having either 0.005%-0.03% Sr or 0.001%-0.01% Na or both added thereto.
According to a thirty-third embodiment of the present invention, the alloy in the first or second embodiments of the present invention is a hypoeutectic Alxe2x80x94Mg alloy containing Mg in an amount not exceeding a maximum solubility limit and which has 0.3%-2.5% Si added thereto.
According to a thirty-fourth embodiment of the present invention, the pressure forming in the first or second embodiments of the present invention is accomplished with the alloy being inserted into a container on an extruding machine.
According to a thirty-fifth embodiment of the present invention, the extruding machine is of either a horizontal or a vertical type or of such a horizontal type in which the container changes position from being vertical to horizontal and the method of extrusion is either direct or indirect.
According to a thirty-sixth embodiment of the present invention, the crystal nuclei in the first embodiment of the present invention are generated by a method in which two or more liquid alloys having different melting points that are maintained superheated to less than 50xc2x0 C. above the liquidus temperature are mixed either directly within the insulated vessel having a heat insulating effect or along a trough in a path into the insulated vessel, such that the temperature of the metal as mixed is either just above or below the liquidus temperature.
According to a thirty-seventh embodiment of the present invention, the two or more metals to be mixed in the thirty-sixth embodiment of the present invention are preliminarily contacted with respective jigs each having a cooling zone such as to produce metals of different melting points that have crystal nuclei and which have attained temperatures just either above or below the liquidus temperature.
According to a thirty-eighth embodiment of the present invention, the top surface of the semisolid metal that is held within the insulated vessel and which is to be fed into the forming mold in the first embodiment of the present invention is removed by means of either a metallic or nonmetallic jig during a period from just after the pouring into the vessel, but before the molding temperature is reached and, thereafter, the semisolid metal is inserted into an injection sleeve.
According to a thirty-ninth embodiment of the present invention, the outer vessel in the eighteenth embodiment of the present invention is heated either from inside or outside or by induction heating, with such heating being performed only or before or after the insertion of the holding vessel into the outer vessel or continued throughout the period not only before, but also after the insertion.
According to a fortieth embodiment of the present invention, the aluminum alloy in the ninth embodiment of the present invention is replaced by a zinc alloy.
With these methods and apparatus of the invention, either liquid or partially solid, partially liquid alloys having crystal nuclei (as exemplified by molten Al and Mg alloys) are charged into an insulated vessel having a heat insulating effect and held there for a period from 5 seconds to 60 minutes as they are cooled to a molding temperature, whereby fine and spherical primary crystals are generated in the solution and the resulting semisolid alloy is fed into a mold, where it is pressure formed to produce a shaped part having a homogeneous microstructure.
Another object of the invention can be attained by a method of shaping a semisolid metal recited in which a liquid alloy having crystal nuclei and at a temperature not lower than the liquidus temperature or a partially solid, partially liquid alloy having crystal nuclei and at a temperature less than the liquidus temperature, but not lower than the molding temperature is poured into a holding vessel having a thermal conductivity of at least 1 kcal/mhxc2x0 C., cooled at an average cooling rate of 0.01xc2x0 C./s-3.0xc2x0 C./s and maintained as such until just prior to the start of shaping under pressure, whereby fine primary crystals are generated in the alloy solution and the alloy within the holding vessel is temperature adjusted by induction heating such that the temperatures of various parts of the alloy fall within the desired molding temperature range for the establishment of a specified liquid fraction no later than the start of shaping and the alloy is recovered from the holding vessel, supplied into a forming mold and shaped under pressure.
The induction heating discussed above is for effecting thermal adjustment such that a specified amount of electric current is applied for a specified time immediately after the pouring of the molten alloy before the representative temperature of the alloy slowly cooling in the holding vessel has dropped to at least 10xc2x0 C. below the desired molding temperature, so that the temperatures of various areas of the alloy within the holding vessel fall within the limits of xc2x15xc2x0 C. of the desired molding temperature.
Once the temperatures of various parts of the alloy within the holding vessel have been adjusted by induction heating to fall within the desired molding temperature range within a specified time, the temperature of the alloy is maintained until just before the start of the shaping step by induction heating at a frequency comparable to or higher than the frequency used in the induction heating for the preceding temperature adjustment.
Either the top portion or the bottom portion or both of the holding vessel can be heat-retained or heated to a higher temperature than the middle portion or the top and bottom portions of the holding vessel are smaller in wall thickness than the middle portion.
The alloy within the holding vessel can be cooled by blowing either air or water or both against said holding vessel from its outside.
Either air or water or both which are at a specified temperature can be blown from at least two different, independently operable heights exterior to the holding vessel such that the blowing conditions and times can be varied freely.
The alloy to be supplied into the forming mold can have a liquid fraction of at least 1.0% but less than 75%.
The crystal nuclei can be generated by vibrating the alloy which builds up in the holding vessel by pouring in a pelt superheated to less than 50xc2x0 C. above the liquidus temperature, the vibration being applied to the alloy either by means of a vibrating rod which is submerged in the melt during its pouring so that it is in direct contact with the alloy or by vibrating not only the vibrating rod, but also the holding vessel as the alloy is poured into said holding vessel.
The crystal nuclei can also be generated by pouring a molten aluminum alloy into the holding vessel, said alloy being held superheated to less than 50% above the liquidus temperature and containing 0.001%-0.01% B and 0.005%-0.3% Ti.
The crystal nuclei can further be generated by pouring a molten magnesium alloy into the holding vessel, the alloy being maintained superheated to less than 50xc2x0 C. above the liquidus temperature and containing 0.01%-1.5% Si and 0.005%-0.1% Sr or 0.05%-0.30% Ca alone.
The invention also concerns a method of shaping a semisolid metal in which a molten aluminum or magnesium alloy containing a crystal grain refiner which is held superheated to less than 50xc2x0 C. above the liquidus temperature is poured directly into a holding vessel without using any cooling jig and held for a period from 30 seconds to 30 minutes as the melt is cooled to the molding temperature where a specified liquid fraction is established such that the temperature of the poured alloy which is liquid and superheated to less than 10xc2x0 C. above the liquidus temperature or which is partially solid, partially liquid and less than 5xc2x0 C. below the liquidus temperature is allowed to decrease from the initial level and pass through a temperature zone 5xc2x0 C. below the liquidus temperature within 10 minutes, whereby fine primary crystals are generated in the alloy solution, and the alloy is recovered from the holding vessel, supplied into a forming mold and shaped under pressure.
The aluminum alloy in the above method can have added thereto 0.03%-0.30% Ti added and can be superheated to less than 30xc2x0 C. above the liquidus temperature as it is poured into the holding vessel.
The aluminum alloy in the above method can have 0.005%-0.3% Ti and 0.001%-0.01% B added thereto and can be superheated to less than 50xc2x0 C. above the liquidus temperature as it is poured into the holding vessel.
The temperature of the alloy poured into the holding vessel can be maintained by temperature adjustment through induction heating such that the temperatures of various parts of said alloy within said holding vessel are allowed to fall within the desired molding temperature range for the establishment of a specified fraction liquid not later than the start of shaping.